The invention relates to a method of manufacturing a semiconductor device whereby a layer comprising aluminium is deposited on a surface of a semiconductor body, into which layer conductor tracks are etched, between which tracks an insulating aluminium compound is provided by a layer of such a material being deposited and subsequently removed by a bulk reducing treatment down to the conductor tracks, after which a layer of insulating material is deposited in which contact windows are etched down to the layer comprising aluminium for local contacting of the conductor tracks.
A plane metallization structure of aluminium conductor tracks which are mutually insulated in the lateral direction by an insulating aluminium compound, such as aluminium oxide or aluminium nitride, is realized by such a method on the surface of the semiconductor body. Such plane metallization structures have long been made by a layer of aluminium being deposited on a stirface of a semiconductor body and is then locally converted into aluminium oxide by means of an anodizing process in, for example, oxalic acid. Such a wet anodizing process does not take place fully anisotropically, so that the oxidation of the aluminium layer in the lateral direction proceeds almost as fast as the oxidation in the thickness direction. As a result, no conductor tracks could be made in this manner suitable for use in integrated circuits with a very high integration density (VLSI). In the method mentioned above, the conductor tracks are etched and the spaces between the conductors are subsequently filled with an insulating aluminium compound. In this manner it is indeed possible to make plane metallization structures which are suitable for such integrated circuits.
The layer comprising aluminium may be a layer of pure aluminium, but may alternatively be a layer of aluminium to which a small quantity of another element or even of several other elements has been added to improve its properties. Usual additives are, for example, a few % by weight of silicon to prevent silicon from a silicon substrate dissolving in the layer comprising aluminium, and a few % by weight of copper to suppress electromigration effects in the layer. These additives, however, render the anodizing oxidation process mentioned above difficult. Copper, for example, is dissolved in oxalic acid so that an undesirable porous layer of aluminium oxide is formed.
U.S. Pat. No. 4,767,724 discloses a method of the kind mentioned in the opening paragraph whereby a deposited layer of aluminium oxide is first planarized, so that the layer has a plane surface which runs substantially parallel to the surface of the semiconductor body. Then the layer is etched away down to the conductor tracks. A metallization structure is thus obtained with a plane surface. A comparatively thin layer of aluminium oxide and a comparatively thick layer of silicon oxide are then deposited on this surface. The comparatively thin layer of aluminium oxide serves as an etching stopper during etching of the contact windows into the layer of silicon oxide. After etching of the contact windows into the layer of silicon oxide, the thin layer of aluminium oxide inside the windows is etched away.
Although conductor tracks suitable for use in integrated circuits with a very high integration density (VLSI) can be made by the known method, this known method also has some disadvantages. Thus planarizing and subsequent etching away of the planarized layer of aluminium oxide down to the aluminium conductor tracks is a process which is difficult to control. Aluminium oxide is etched in a plasma containing boron chloride. At the end of the etching process, when the aluminium oxide has just been removed from the aluminium tracks, these tracks will also be etched in such a plasma. Since such an etching process does not take place equally fast everywhere, seen over the entire surface of the semiconductor body, the conductor pattern may become strongly etched locally to an undesirable extent. A similar problem occurs once more when the comparatively thin layer of aluminium oxide which serves as an etching stopper and which is still present inside the contact windows after etching of the layer of silicon oxide, is to be etched away.